GEOLOGY AND PALEONTOLOGY. Lf 
wanting and the balls rest directly upon the ground. They cover a space of per- 
haps two acres; and when seen from a distance present the appearance of a mili- 
tary encampment, or even of a city, whence the name. The masses are ordinarily 
globular, from fifteen to twenty feet in diameter, and have the general appearance 
of an Eskimo hut. They are often so close together that a person may step from 
one to the other. In some places are passageways wide enough for a wagon to 
pass through. All stages of formation and erosion may be seen, from the stage 
where the top of a boulder is just protruding from a bank, through forms that 
are only half uncovered, and complete globes, to those that have fallen to pieces 
and are weathering away. Table rock, in Lincoln county, Kansas, until recently 
exhibited the same peculiarities of form that are seen in Pulpit rock to-day, 
but has now fallen down. (See plate XI.) These are all pronounced erosion 
forms; and as such are of more than usual interest both to the geologist and to. 
the ordinary observer. 
In lithological character the hard ledges mentioned above approach a quartz- 
ite. There are several such ledges in the Dakota. In eastern Saline and north- 
ern McPherson counties, Kansas, quartzite boulders are not infrequent. Doctor 
Hayden refers to numerous layers from one to four feet thick, of a very compact,. 
massive quartzite, at the Blackbird mission, Nebraska. Doctor Barbour and the 
writer, in October, 1890, visited a ledge of extremely hard and massive quartzite- 
like rock five miles northwest of Fairbury, Jefferson county, Nebraska. This. 
ledge is gray in color, and consists of very fine grains of sand cemented with cal- 
cium. These ledges all produce an excellent building stone, and will be discussed 
more in detail under ‘‘ Economic Phase.’’ 
One of the most peculiar forms of Dakota stratigraphy is found in the gravel- 
beds on the Platte river, at Cedar Creek and Springfield, Neb. At this point 
the Dakota rests on the unevenly eroded surface of the Carboniferous. The line 
of contact between the two groups sometimes differs as much as seventy-five 
feet in elevation in a few hundred yards. In those long-gone Mesozoic times the 
hills were evidently as high and the hollows as deep as those of the present time. 
It is in one of the lowest of these hollows that the gravel-bed has been deposited. 
The best exposure is a mile west of Cedar Creek, at which place the railroad has 
run a spur along the base of the hill for the purpose of obtaining gravel. The 
lower twenty feet of the Dakota consists of an extremely hard conglomerate, ar- 
ranged in layers, which are usually cross-bedded and interspersed between ledges 
of typical brown sandstone. The conglomerate is composed of hard, water-worn 
pebbles of quartz, feldspar, granite, etc., varying in size from fine sand to the 
size of a walnut. These pebbles are cemented together by silicon into a rock 
which is so hard as to be broken with great difficulty. The form and color is so 
peculiar as to obtain for it the characteristic name ‘‘ peanut rock.’? Above the 
hard conglomerate at the base of the group is found from twenty to forty feet of 
loose gravel and sand. It differs from the lower ledge chiefly in the size of the 
pebbles and the relatively smaller amount of cementing material. The pebbles 
are rarely larger than pigeons’ eggs, and are so loosely cemented together that 
the material may often be removed with a scraper. The bank shows all grada- 
tions from coarse gravel to very fine sand, and is in most places more or less 
cross-bedded. There are some ledges of typical Dakota sandstone and a few 
fragments of silicified wood, but no leaf remains have been found. 
It is probable that the gravel-beds mark the location of an ancient Dakota 
river, The lines of cross-bedding usually incline toward the southwest, indicat- 
ing that the current came from the northeast, which agrees with our ideas of the 
origin of Dakota deposits. It is a matter of common observation that, while 
